Humans can hold their breath longer than “

In his current training, he said, he does exercises every morning in which he breathes for no more than 12 minutes over the course of an hour, and he sleeps in a hypoxic tent in his Manhattan apartment that simulates the thin air at 15,000 feet above sea level.

He has been concentrating on lowering his oxygen consumption by slowing his metabolism, partly through diet (he fasted for 18 hours before the breath-hold in the pool) and partly through relaxation. In a test by Dr. Potkin, Mr. Blaine on command quickly lowered his heart rate by 25 percent.

“David seems to have a phenomenal ability, like Buddhist monks, to control his body,” Dr. Potkin said.

And I didn’t appreciate how much progress free divers and their coaches have made at pushing the limits of human endurance until Mr. Blaine put my time in perspective. “Houdini used to brag about going three and a half minutes underwater,” Mr. Blaine said. “Look at how easily you beat Houdini.”